The origin of lattice instability in bcc tungsten under triaxial loading

Abstract

Stability of ideal bcc tungsten crystal under triaxial tensile loading was explored from first principles using an analysis of both elastic and dynamic stability. The triaxial stress state was considered as a superposition of axial and biaxial transverse stresses. The region of attainable stresses which was delimited using the computed tensile stress maxima was marginally reduced by occurrence of soft phonons in the crystal lattice. While, under purely hydrostatic tension, the crystal was predicted stable up to 48 GPa, greater magnitude of a differential stress reduced the value of a mean (hydrostatic) stress associated with first phonon instabilities to about 35 GPa. This value is rather close to that recently determined in experiment. Computed phonon spectra were successfully verified with the help of atomistic models of microscopic lattice deformation.

Keywords:

• Theoretical strength
• triaxial loading
• stress superposition
• soft phonons
• ab initio calculations

Notes

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research has been financially supported by the Czech Science Foundation [project number GA 17-18566S]; by the Ministry of Education, Youth and Sports of the Czech Republic under the project CEITEC 2020 [grant number LQ1601].